Alkaline storage cell and hydrogen storage alloy for negative electrode of alkaline storage cell

Abstract

An alkaline storage cell has a positive electrode, a negative electrode containing a hydrogen storage alloy, and an alkaline electrolyte. The hydrogen storage alloy has a composition expressed by a general expression: Ln 1-α Mg α Ni β-γ-δ T γ Al δ , where Ln represents at least one element chosen from a group consisting of La, Ce, etc., T represents at least one element chosen from a group consisting of V, Nb, etc., and subscripts α, β, γ and δ represent numerical values which satisfy 0.05<α<0.12, 3.40≦β≦3.70, 0.01≦γ≦0.15 and 0.15≦δ≦0.35.

1. An alkaline storage cell comprising:
 a positive electrode; 
 an alkaline electrolyte; and 
 a negative electrode containing a hydrogen storage alloy, the hydrogen storage alloy having a composition expressed by a general expression:
   Ln 1-α Mg α Ni β-γ-δ T γ Al δ   
 
 
       (where Ln represents at least one element chosen from a group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf, T represents at least one element chosen from a group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Zn, Ga, Sn, In, Cu, Si, P and B, and subscripts α, β, γ and δ represent numerical values which satisfy
   0.05<α<0.12, 
   3.40≦β≦3.70, 
   0.01≦γ≦0.15 and 
   0.15≦δ≦0.35); 
 wherein the hydrogen storage alloy includes
 a parent phase, in the parent phase a ratio (Cmin/Cave) of a minimum concentration (Cmin) of Mg to an average concentration (Cave) of Mg being greater than or equal to 0.4, and 
 segregation phases, an area ratio of the segregation phases in a cross section of the hydrogen storage alloy being less or equal to 30%. 
 
 
     
     
       2. The cell according to  claim 1 , wherein the area ratio of the segregation phases in the cross section of the hydrogen storage alloy is less than or equal to 25%. 
     
     
       3. The cell according to  claim 2 , wherein the area ratio of the segregation phases in the cross section of the hydrogen storage alloy is less than or equal to 10%. 
     
     
       4. The cell according to  claim 1 , wherein α in the expression is in a range 0.06<α<0.10. 
     
     
       5. The cell according to  claim 4 , wherein α in the expression is in a range 0.06<α≦0.09. 
     
     
       6. The cell according to  claim 5 , wherein the area ratio of the segregation phases in the cross section of the hydrogen storage alloy is less than or equal to 25%. 
     
     
       7. The cell according to  claim 6 , wherein the area ratio of the segregation phases in the cross section of the hydrogen storage alloy is less than or equal to 10%. 
     
     
       8. A hydrogen storage alloy for a negative electrode of an alkaline storage cell, having composition expressed by a general expression:
   Ln 1-α Mg α Ni β-γ-δ T γ Al δ   
 (where Ln represents at least one element chosen from a group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ca, Sr, Sc, Y, Ti, Zr and Hf, T represents at least one element chosen from a group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Zn, Ga, Sn, In, Cu, Si, P and B, and subscripts α, β, γ and δ represent numerical values which satisfy 0.05<α<0.12, 3.40≦β≦3.70, 0.01≦γ≦0.15 and 0.15≦δ≦0.35); 
 wherein the hydrogen storage alloy includes
 a parent phase, in the parent phase a ratio (Cmin/Cave) of a minimum concentration (Cmin) of Mg to an average concentration (Cave) of Mg being greater than or equal to 0.4, and 
 segregation phases, an area ratio of the segregation phases in a cross section of the hydrogen storage alloy being less than or equal to 30%. 
 
 
     
     
       9. The hydrogen storage alloy according to  claim 8 , wherein the area ratio of the segregation phases in the cross section of the hydrogen storage alloy is less than or equal to 25%. 
     
     
       10. The hydrogen storage alloy according to  claim 9 , wherein the area ratio of the segregation phases in the cross section of the hydrogen storage alloy is less than or equal to 10%. 
     
     
       11. The hydrogen storage alloy according to  claim 8 , wherein α in the expression is in a range 0.06<α<0.10. 
     
     
       12. The hydrogen storage alloy according to  claim 11 , wherein α in the expression is in a range 0.06<α≦0.09. 
     
     
       13. The hydrogen storage alloy according to  claim 12 , wherein the area ratio of the segregation phases in the cross section of the hydrogen storage alloy is less than or equal to 25%. 
     
     
       14. The hydrogen storage alloy according to  claim 13 , wherein the area ratio of the segregation phases in the cross section of the hydrogen storage alloy is less than or equal to 10%.